An injection device having a dose indicating drum and a drive spring is known from the prior art, namely WO 2008/031237 A1. The drive spring is a coiled spring, which is wound in a spiral shape from a strip-shaped material. When the product dose is being set, the spring is cocked with a rotary movement. In order to dispense a dose, a piston rod is coupled to the spring by means of an actuating knob at the proximal end of the device, whereby the spring can output the energy stored therein to the piston rod, whereby the piston rod is moved in the dispensing direction. To set a new dose, the spring is again cocked by rotating the dosing knob, and so on. This is repeated until the product container has been emptied.
European Patent Application No. 12 162 777.2 describes a driving and dosing device as shown in the attached FIGS. 1-5c. This device has a drive spring, which is preloaded with sufficient energy in the delivery state of the driving and dosing device that it can dispense the dispensable quantity of product from the product container in multiple individual dispensing strokes. The dispensing spring drives a rotary member, the rotation of which causes a propulsion member to displace the piston of a product container, whereby the product contained in the product container is dispensed. To dispense the product, a pushbutton is actuated, whereby a closed clutch is opened, the opened clutch allowing the rotation of the rotary member and the closed clutch not allowing the rotation of the rotary member.
Such injection devices presume that the preloaded dispensing spring starts the dispensing of the product without further effort when the actuating knob or pushbutton has been completely actuated. Since such injection devices are occasionally stored for a long time prior to use, it is possible for the mechanism to become “stuck” or not properly release when the actuating knob has been completely actuated, so that dispensing of the product starts with a delay or only starts when a slight tap (mechanical shock) is applied to the injection device.